You can discuss different forms of measurement--inches, feet, and yards in the US and millimeters, centimeters, and meters almost everywhere else.

A screwdriver...

Most common ones are the Flat head and Phillips head. If anyone has bought something at IKEA you probably had a little lesson with them.

You can teach clockwise to tighten and counter-clockwise to loosen (although plumbing can be the opposite).

An Allen wrench set...

See how many furniture pieces you have that use this. I know I use my set a lot for bathroom fixtures. For an activity get some screws that have the hex indentation and see if the kids can find the correct wrench they need.

A combination wrench (I had to look on Wikipedia for the name of this one since I forgot)

If you ever have a bike to put together you will need one of these... For an activity you can pick up hex screws at your hardware store and make see how many complete turns you can do before the screw is in the wood.